I found this: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=a07730472c49c1f7bb56afa3eb8be23e6e87b4f1
but there is no specific image for the EA9500 available.
Looking at Build for Linksys EA9500 the support status should be at least "External image". I will create a dataentry for this device later.